Solar energy conversion systems translate solar radiant energy into a useable form, such as thermal energy or electricity through solar array panels. In one process, the solar radiant energy is converted into thermal energy by focusing the sun's rays on a fluid, which is then used for power generation through the use of steam generation to drive turbines of electrical generators. Alternatively, the solar radiant energy is converted directly into electricity through the use of photovoltaic collection systems. Solar arrays are used for a wide variety of purposes, including as a utility power system, as a power supply for a remote or unmanned site, etc. A solar array's capacity ranges from a few kilowatts to a hundred kilowatts or more, and is capable of being installed wherever there is an area with exposure to the sun for significant portions of the day.
Utility power systems typically include solar arrays that are either direct or concentrating systems. The direct systems receive incident light directly from the sun's radiant energy and generate current. The direct systems typically include large arrays of photovoltaic cells. Conversely, the concentrating systems reflect the sun's incident light and either concentrate it onto an array of photovoltaic cells or heat a fluid that can then be used for power generation.
There are multiple ways of positioning solar arrays to track the sun. Some solar arrays have panels positioned in rows supported on a torque tube that serves as an axis of rotation. A drive system rotates or rocks the rows to keep the panels directed at the sun. Usually, the rows are arranged with their axes disposed in a north-south direction, and the drive system gradually rotates the rows of panels throughout the day from an east-facing direction in the morning to a west-facing direction in the afternoon. The rows of panels are brought back to the east-facing orientation for the next day of operation. Other panels have a two-directional axis of rotation around both the vertical and horizontal axis to allow the panels to rotate and tilt in order to maximize their exposure to the sun's solar radiant energy. A drive system is mounted on the panel axes to position the solar arrays in the proper directions.
In most solar arrays, a tracking system is employed to control the positioning of the concentrators as a function of the diurnal rotation and seasonal changes in orientation of the Earth relative to the sun. To maximize the radiant energy incident on the cells, mirror, lenses, etc., the arrays need to be positioned as accurately as possible toward the sun. For example, positioning the array in concentrator systems is important because the area of sun concentration may have an effective area of less than one percent (1%) of that required for direct systems. For the concentrator systems, an error of only one half degree of arc represents a misaiming of more than one solar diameter, which in some concentrator systems is unacceptable.
Some systems employ a sun sensor to provide feedback regarding positioning of the array relative to the sun. During evening hours or cloudy weather, when available solar energy is diminished, the solar arrays may become misoriented with respect to the sun. In order to conserve energy, the solar arrays are moved as little as possible, because every time the solar arrays are moved even a fraction of an inch, large amounts of power are used. When the sun appears again, the control system must be able to reorient the solar arrays over a wide angular range relative to the axis. Thus, improving the accuracy of the orientation of a solar array relative to the sun can significantly increase the efficiency of photovoltaic cells and/or concentrator systems.
To be practical the array positioning control systems for either direct or concentrator systems should be accurate, but inexpensive to help offset the high costs of solar arrays. This precludes certain designs that otherwise might be attractive. For example, a clock driven system could be employed in which the array is driven by the time of day only. However, such a system could not tolerate slippage in array positioning without resulting in misaiming. Such a non-slip system would require a solar array system rigid enough to withstand the anticipated wind loading. Such rigidity implies a bulky and expensive drive mechanism which makes the system very costly.
For this reason, many of the direct and concentrating control systems include various mechanical inclinometers used to detect positional changes in the movement of the solar array in combination with a sun sensor to detect the position of the sun. Inclinometers are used to detect angular inclination or displacement of the solar arrays. The reference is typically supplied by the gravitational pull of the Earth. The inclinometers that have been used in tracking systems in the past are often expensive, do not have the desired functionality and tolerances across applications, require frequent calibration, and are prone to failures due to the lack of durability, all of which result in increased costs.
There is a need to develop systems and methods to improve the control and tracking systems of various solar arrays, which will, in turn, improve the reliability, cost, and efficiency of the solar arrays.